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Ch.18 - Free Energy and Thermodynamics
Tro - Chemistry: A Molecular Approach 4th Edition
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Tutti i libri di testoTro 4th EditionCh.18 - Free Energy and ThermodynamicsProblema 56b
Capitolo 18, Problema 56b

Use data from Appendix IIB to calculate ΔS°rxn for each of the reactions. In each case, try to rationalize the sign of ΔS°rxn. b. Cr2O3(s) + 3 CO(g) → 2 Cr(s) + 3 CO2(g)

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Identify the standard entropy values (S°) for each reactant and product from Appendix IIB.
Write the balanced chemical equation: Cr2O3(s) + 3 CO(g) → 2 Cr(s) + 3 CO2(g).
Calculate the total standard entropy of the reactants: S°(reactants) = S°(Cr2O3) + 3 * S°(CO).
Calculate the total standard entropy of the products: S°(products) = 2 * S°(Cr) + 3 * S°(CO2).
Determine the change in standard entropy for the reaction: ΔS°rxn = S°(products) - S°(reactants).

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Standard Entropy (ΔS°)

Standard entropy (ΔS°) is a measure of the disorder or randomness in a system at standard conditions (1 bar, 25°C). It quantifies the amount of energy that is unavailable to do work due to the dispersal of energy among the available microstates of a system. Higher entropy values indicate greater disorder, while lower values suggest more order.
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Standard Molar Entropy

Entropy Change in Reactions

The change in entropy (ΔS°rxn) for a chemical reaction is calculated by subtracting the total standard entropies of the reactants from those of the products. A positive ΔS°rxn indicates an increase in disorder, often associated with the production of gas from solids or liquids, while a negative ΔS°rxn suggests a decrease in disorder, typically when gases are converted to solids or liquids.
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Entropy in Phase Changes

Rationalizing the Sign of ΔS°rxn

Rationalizing the sign of ΔS°rxn involves analyzing the physical states and the number of moles of reactants and products. For example, in the reaction given, the conversion of solid Cr2O3 and gaseous CO to solid Cr and gaseous CO2 results in a net increase in the number of gas molecules, which typically leads to a positive ΔS°rxn, indicating increased disorder in the system.
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Spontaneity of Reactions
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